This invention relates to a method of correcting distortion in a linear scanning X-ray system, and to apparatus for implementing the method.
Linear scanning X-ray systems are known which comprise a radiation source mounted at one end of a C-shaped arm for generating an imaging beam, a detector at an opposed end of the C-arm responsive to the imaging beam to generate an output signal, and a drive arranged to move at least one of the radiation source and the detector relative to a subject in a scanning direction. Such systems are typically used for the acquisition of whole-body images of a patient or other subject, as described in U.S. Pat. No. 6,921,200 or International patent application no. WO 00/53093.
For example, such apparatus can be used provide fast X-ray images of injured patients. Once a patient has been stabilized, he or she can conveniently be placed on a trolley or gurney, placed in position, scanned, and wheeled out for further treatment, with the resulting radiograph appearing on the diagnostic screen virtually instantaneously. Due to the low X-ray dose administered by the apparatus, the risk of radiation exposure to staff and patients is reduced.
X-ray images from such apparatus contain a non-linear distortion that must be corrected for critical applications. This distortion is a result of the imaging process: X-rays from a point source are spread out into a fan beam before being captured by a detection device such as a photographic plate or an electronic CCD sensor.
Because of this, objects closer to the centre of the detector suffer less distortion than those at the edges. This makes the correction process a non-trivial task, traditionally requiring multiple scans to be taken and stitched together manually to minimise the distortion. The distortion correction of X-ray images is of particular interest in certain medical fields, particularly for prosthetics, implants, and orthopaedic work.
It would be desirable to be able to take accurate measurements directly from X-ray images, and that these images should be obtained with a minimum of patient discomfort and exposure to radiation.